Objective: There is increasing interest regarding the risk and overlap of executive function deficits (EFDs) in stable cigarette smoking and substance use disorders (SUD). Therefore, we examined whether earlier EFD was a risk factor for subsequent cigarette smoking and SUD and further explored the relationship between EFD and SUD. Method: We assessed 435 subjects at the 5-year follow-up (232 subjects with attention-deficit/hyperactivity disorder [ADHD], mean age plus or minus SD: 15.4 plus or minus 3.43 years; and 203 controls: 16.3 [plus or minus] 3.42 years) and again 4 to 5 years later as part of a prospective family study of youth with ADHD. Individuals were assessed by structured psychiatric interview for psychopathology and SUD. EFD was categorically defined in an individual who had abnormal results on at least two of six neuropsychological tests of executive functioning. Results: At the final follow-up period, ADHD was found to be a significant predictor of stable cigarette smoking (p less than 0.01) and SUD into late adolescence and young adult years (p less than 0.01). However, EFDs were not associated with an increase in subsequent substance use outcomes. New-onset stable cigarette smoking, but not SUD, was associated with subsequent EFD (p less than 0.01). Conclusions: Our results do not support the hypothesis that EFDs predicts later stable cigarette smoking or SUD in children with ADHD growing up. However, stable cigarette smoking is associated with subsequent EFD. (Contains 2 tables.)